On Mon, 26 Oct 2015 11:28:04 +1100, Clifford Heath <no.spam@please.net> wrote:>On 26/10/15 08:30, John Larkin wrote: >> On Sun, 25 Oct 2015 10:46:35 -0700 (PDT), kellysbradbury@gmail.com >> wrote: >> >>> On Saturday, October 24, 2015 at 7:06:57 AM UTC-6, kellysb...@gmail.com wrote: >>>> I am having a difficult problem on a current project so I was wondering if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controller connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like platinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio? >>>> >>>> -Kelly >>> >>> >>> Thanks everyone for your responses! To answer some of your questions: >>> >>> I am going to about 1050 C in an oxidizing atmosphere so that rules out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding. >>> >>> I don't have to make fast measurements, in fact 1 sample measurement per second would be fine. >>> >>> I have tried ramping to a certain temperature and then unplugging the furnace. All the noise goes away and I can get continuous data with no problem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution. >>> >>> Someone suggested an isolation transformer but that might be cost prohibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics store but I haven't tried it yet. >>> >>> I like the idea of integrating a capacitor. Texas Instruments makes the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time. >>> >>> Thanks in advance! I really appreciate all your responses. >>> >>> Kelly >> >> You could use a small DPDT relay and a capacitor as a flying-cap >> integrator. Connect the cap to the input leads for one second; then >> switch it to a DVM and measure the voltage for 100 ms or whatever; > >What about timing jitter in the relay?A nice small relay will operate in a millisecond or so, so the jitter must be in the 100 us ballpark. That's 100 PPM error out of a second of integration.
measuring nanoamps with lots of noise
Started by ●October 24, 2015
Reply by ●October 25, 20152015-10-25
Reply by ●October 26, 20152015-10-26
On Saturday, October 24, 2015 at 4:48:21 PM UTC-4, dca...@krl.org wrote:> On Saturday, October 24, 2015 at 9:06:57 AM UTC-4, kellysb...@gmail.com wrote: > > The furnace is controlled by a PID temp controller connected to a solid state relay. > > > > -Kelly > > Check your PID temp controler. I think some have a output for a SSR and also an output for a regular relay. If so you could switch to a regular relay and DC for the heating power. Add an one shot and a and circuit so the temp reading can only occur with the heater either on or off , but not when the relay is changing state. > > DanThat's a good approach. I'd bet the worst noise is zero-crossings in the solid state relay, and you laid out a nice test for that. The ultimate noise elimination test would be to power the thing with variable DC, such as a rectifier / filter and a variac. That eliminates both potential PID controller noise, and the SSR. Once electromagnetic interference is reduced as far as possible, shielding might be considered. This reference suggests 310 stainless as suitable for oxidizing atmospheres up to 1,100C. http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/proc_heat_tech_brief.pdf IIRC it's available as foil, used to wrap parts when heat-treating steel. Cheers, James Arthur
Reply by ●October 26, 20152015-10-26
On Sunday, October 25, 2015 at 11:21:07 PM UTC-4, dagmarg...@yahoo.com wrote:> On Saturday, October 24, 2015 at 4:48:21 PM UTC-4, dca...@krl.org wrote: > > On Saturday, October 24, 2015 at 9:06:57 AM UTC-4, kellysb...@gmail.com wrote: > > > The furnace is controlled by a PID temp controller connected to a solid state relay. > > > > > > -Kelly > > > > Check your PID temp controler. I think some have a output for a SSR and also an output for a regular relay. If so you could switch to a regular relay and DC for the heating power. Add an one shot and a and circuit so the temp reading can only occur with the heater either on or off , but not when the relay is changing state. > > > > Dan > > That's a good approach. I'd bet the worst noise is zero-crossings in the > solid state relay, and you laid out a nice test for that. > > The ultimate noise elimination test would be to power the thing with > variable DC, such as a rectifier / filter and a variac. That eliminates > both potential PID controller noise, and the SSR. > > Once electromagnetic interference is reduced as far as possible, shielding > might be considered. This reference suggests 310 stainless as suitable for > oxidizing atmospheres up to 1,100C. > http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/proc_heat_tech_brief.pdf > > IIRC it's available as foil, used to wrap parts when heat-treating steel.My mistake, the foil is 309 SS, not 310. Rated to 1,200C by this vendor: http://www.keithcompany.com/heat-treat-foils-and-tool-wraps.html Cheers, James Arthur
Reply by ●October 26, 20152015-10-26
On Sunday, October 25, 2015 at 1:46:40 PM UTC-4, kellysb...@gmail.com wrote:> On Saturday, October 24, 2015 at 7:06:57 AM UTC-6, kellysb...@gmail.com wrote: > > I am having a difficult problem on a current project so I was wondering if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controller connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like platinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio? > > > > -Kelly > > > Thanks everyone for your responses! To answer some of your questions: > > I am going to about 1050 C in an oxidizing atmosphere so that rules out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding. > > I don't have to make fast measurements, in fact 1 sample measurement per second would be fine. > > I have tried ramping to a certain temperature and then unplugging the furnace. All the noise goes away and I can get continuous data with no problem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution. > > Someone suggested an isolation transformer but that might be cost prohibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics store but I haven't tried it yet. > > I like the idea of integrating a capacitor. Texas Instruments makes the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time. > > Thanks in advance! I really appreciate all your responses.Can you look at the noise/ interference on a 'scope? (or are the signals too small?) If you knew it was 60 Hz, or a switching transient or something else then that would help. George H.> > Kelly
Reply by ●October 26, 20152015-10-26
On Monday, October 26, 2015 at 10:03:50 AM UTC-4, George Herold wrote:> On Sunday, October 25, 2015 at 1:46:40 PM UTC-4, kellysb...@gmail.com wrote: > > On Saturday, October 24, 2015 at 7:06:57 AM UTC-6, kellysb...@gmail.com wrote: > > > I am having a difficult problem on a current project so I was wondering if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controller connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like platinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio? > > > > > > -Kelly > > > > > > Thanks everyone for your responses! To answer some of your questions: > > > > I am going to about 1050 C in an oxidizing atmosphere so that rules out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding. > > > > I don't have to make fast measurements, in fact 1 sample measurement per second would be fine. > > > > I have tried ramping to a certain temperature and then unplugging the furnace. All the noise goes away and I can get continuous data with no problem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution. > > > > Someone suggested an isolation transformer but that might be cost prohibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics store but I haven't tried it yet. > > > > I like the idea of integrating a capacitor. Texas Instruments makes the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time. > > > > Thanks in advance! I really appreciate all your responses. > > Can you look at the noise/ interference on a 'scope? > (or are the signals too small?) > If you knew it was 60 Hz, or a switching transient or > something else then that would help. > > George H. > > > > KellyIf it were a zero-crossing SSR, integrating over an integer number of line cycles would help a lot, theoretically. (Avoids the problem of the PID switching asynchronously to the integration interval.) Cheers, James
Reply by ●October 26, 20152015-10-26
On Mon, 26 Oct 2015 08:11:45 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Monday, October 26, 2015 at 10:03:50 AM UTC-4, George Herold wrote: >> On Sunday, October 25, 2015 at 1:46:40 PM UTC-4, kellysb...@gmail.com wrote: >> > On Saturday, October 24, 2015 at 7:06:57 AM UTC-6, kellysb...@gmail.com wrote: >> > > I am having a difficult problem on a current project so I was wondering if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controller connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like platinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio? >> > > >> > > -Kelly >> > >> > >> > Thanks everyone for your responses! To answer some of your questions: >> > >> > I am going to about 1050 C in an oxidizing atmosphere so that rules out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding. >> > >> > I don't have to make fast measurements, in fact 1 sample measurement per second would be fine. >> > >> > I have tried ramping to a certain temperature and then unplugging the furnace. All the noise goes away and I can get continuous data with no problem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution. >> > >> > Someone suggested an isolation transformer but that might be cost prohibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics store but I haven't tried it yet. >> > >> > I like the idea of integrating a capacitor. Texas Instruments makes the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time. >> > >> > Thanks in advance! I really appreciate all your responses. >> >> Can you look at the noise/ interference on a 'scope? >> (or are the signals too small?) >> If you knew it was 60 Hz, or a switching transient or >> something else then that would help. >> >> George H. >> > >> > Kelly > >If it were a zero-crossing SSR, integrating over an integer number of >line cycles would help a lot, theoretically. (Avoids the problem of the >PID switching asynchronously to the integration interval.) > >Cheers, >JamesTo invoke filtering of any sort, you'd have to know that the current source is constant or linear on voltage. If it is a semiconductor sort of thing, it will rectify the noise and mess up the average current measurement.
Reply by ●October 26, 20152015-10-26
On Monday, October 26, 2015 at 11:11:51 AM UTC-4, dagmarg...@yahoo.com wrote:> On Monday, October 26, 2015 at 10:03:50 AM UTC-4, George Herold wrote: > > On Sunday, October 25, 2015 at 1:46:40 PM UTC-4, kellysb...@gmail.com wrote: > > > On Saturday, October 24, 2015 at 7:06:57 AM UTC-6, kellysb...@gmail.com wrote: > > > > I am having a difficult problem on a current project so I was wondering if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controller connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like platinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio? > > > > > > > > -Kelly > > > > > > > > > Thanks everyone for your responses! To answer some of your questions: > > > > > > I am going to about 1050 C in an oxidizing atmosphere so that rules out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding. > > > > > > I don't have to make fast measurements, in fact 1 sample measurement per second would be fine. > > > > > > I have tried ramping to a certain temperature and then unplugging the furnace. All the noise goes away and I can get continuous data with no problem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution. > > > > > > Someone suggested an isolation transformer but that might be cost prohibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics store but I haven't tried it yet. > > > > > > I like the idea of integrating a capacitor. Texas Instruments makes the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time. > > > > > > Thanks in advance! I really appreciate all your responses. > > > > Can you look at the noise/ interference on a 'scope? > > (or are the signals too small?) > > If you knew it was 60 Hz, or a switching transient or > > something else then that would help. > > > > George H. > > > > > > Kelly > > If it were a zero-crossing SSR, integrating over an integer number of > line cycles would help a lot, theoretically. (Avoids the problem of the > PID switching asynchronously to the integration interval.)Yup, It's hard to know. Noise/interference (as you know) is like an onion, you can think about all these sources. But practically you need to know which is on the outside layer. George H.> > Cheers, > James
Reply by ●October 26, 20152015-10-26
On Sunday, October 25, 2015 at 8:21:07 PM UTC-7, dagmarg...@yahoo.com wrote:> Once electromagnetic interference is reduced as far as possible, shielding > might be considered. This reference suggests [310] stainless as suitable for > oxidizing atmospheres up to 1,100C. > http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/proc_heat_tech_brief.pdf > > IIRC it's available as foil, used to wrap parts when heat-treating steel.Another candidate is Inconel (600, 601, 625...); chrome-nickel 'superalloys' that stays intact to 1900C
Reply by ●October 26, 20152015-10-26
On Monday, October 26, 2015 at 11:43:40 AM UTC-4, John Larkin wrote:> On Mon, 26 Oct 2015 08:11:45 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > > >On Monday, October 26, 2015 at 10:03:50 AM UTC-4, George Herold wrote: > >> On Sunday, October 25, 2015 at 1:46:40 PM UTC-4, kellysb...@gmail.com wrote: > >> > On Saturday, October 24, 2015 at 7:06:57 AM UTC-6, kellysb...@gmail.com wrote: > >> > > I am having a difficult problem on a current project so I was wondering if anyone could help. This is a project where I have to measure current generated by a sample at high temperature inside a furnace. The current is in the picoamp-nanoamp range depending on temperature and I have been using a Keithley picoammeter. The furnace is controlled by a PID temp controller connected to a solid state relay. When the relay is off I can get data with no issues but when the relay is on there is lots of noise and I cannot get good data. Unfortunately, the high temperature environment makes it difficult to shield the sample without going to exotic materials like platinum foil. Is it possible to measure picoamps-nanoamps in the presence of lots of noise by using some kind of instrumentation amplifier or something with very good common mode rejection ratio? > >> > > > >> > > -Kelly > >> > > >> > > >> > Thanks everyone for your responses! To answer some of your questions: > >> > > >> > I am going to about 1050 C in an oxidizing atmosphere so that rules out many traditional materials. Basically I have to use platinum wires to connect to the sample. Nobody that I know makes a high temp coax that goes to 1050 C which is why I have virtually no shielding. > >> > > >> > I don't have to make fast measurements, in fact 1 sample measurement per second would be fine. > >> > > >> > I have tried ramping to a certain temperature and then unplugging the furnace. All the noise goes away and I can get continuous data with no problem. But that is not a good long term solution since I will need to record data over multiple ramp/dwell/cool cycles which is why I am looking for a better solution. > >> > > >> > Someone suggested an isolation transformer but that might be cost prohibitive and same goes for a DC power supply. My furnace runs off 120 V at 14 amps. However, I did find a line filter at the local surplus electronics store but I haven't tried it yet. > >> > > >> > I like the idea of integrating a capacitor. Texas Instruments makes the IVC102 which does this but I am sure there are other solutions as well. Has anyone used this IC? Are there other IC's or solutions that someone could recommend? I will be honest, my electronics skills are amateur but I have breadboarded a few things in my time. > >> > > >> > Thanks in advance! I really appreciate all your responses. > >> > >> Can you look at the noise/ interference on a 'scope? > >> (or are the signals too small?) > >> If you knew it was 60 Hz, or a switching transient or > >> something else then that would help. > >> > > > >If it were a zero-crossing SSR, integrating over an integer number of > >line cycles would help a lot, theoretically. (Avoids the problem of the > >PID switching asynchronously to the integration interval.) > > To invoke filtering of any sort, you'd have to know that the current > source is constant or linear on voltage. If it is a semiconductor sort > of thing, it will rectify the noise and mess up the average current > measurement.You're right, I'd assumed the EMI wasn't interacting with the signal source. The furnace itself is typically a brick-lined steel box, which you'd think would be pretty good first-order shielding from the outside world. With these high impedances, capacitive-coupling from the heating element could be serious; an electrostatic shield could fix that. The easy solution is just to turn the thing off for the one-second measurement interval. The thermal time constant is so much longer that 1s shouldn't make a nit's difference to temperature control. Cheers, James
Reply by ●October 26, 20152015-10-26
On Monday, October 26, 2015 at 2:54:53 PM UTC-4, whit3rd wrote:> On Sunday, October 25, 2015 at 8:21:07 PM UTC-7, dagmarg...@yahoo.com wrote: > > > > Once electromagnetic interference is reduced as far as possible, shielding > > might be considered. This reference suggests [310] stainless as suitable for > > oxidizing atmospheres up to 1,100C. > > http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/proc_heat_tech_brief.pdf > > > > IIRC it's available as foil, used to wrap parts when heat-treating steel. > > Another candidate is Inconel (600, 601, 625...); chrome-nickel 'superalloys' that > stays intact to 1900COnline Metals has some for only $120/ft^2 (!) http://www.onlinemetals.com/merchant.cfm?pid=9820&step=4&showunits=inches&id=337&top_cat=1352 (Earlier this year I passed on what must have been 150lbs of Inconel for $5/lb--I had no way to melt it!) Cheers, James Arthur